Transcript (Viability) Assessment and Measures of Success

Conservation Target Integrity
(Viability) Assessment and
Measures of Success:
THEORETICAL FOUNDATIONS
AND CHALLENGES
David P. Braun
Robert S. Unnasch
Jeffrey D. Parrish
June, 2003
Four foundation elements
1 “Key attributes” of target viability/integrity
2 Indicators for key attributes
3 “Acceptable range of variation” (ARV) and
its critical ecological thresholds/limits
4 Data “roll-up”:
indicatorsattributesscorecard group
target
Four foundation elements
1 “Key attributes” of target viability/integrity
2 Indicators for key attributes
3 “Acceptable range of variation” (ARV) and
its critical ecological thresholds/limits
2 Data “roll-up”:
indicatorsattributesscorecard group
target
Theory (1):
“Key ecological attributes”
Attributes of a target’s biotic structure & composition,
ecological processes, environmental regimes & constraints,
and landscape structure that...
• Characterize its biotic structure and composition
• Limit its spatial distribution
• Exert pivotal causal influence on other attributes
• Drive temporal variation in structure, composition,
distribution
• Contribute significantly to resistance and resilience
• Determine sensitivity to human impacts
Key ecological attributes: Chinook salmon (Oncorhynchus
tshawytscha), Cosumnes River Project, CA
Theory (2):
“Key ecological attributes”
Foundation: cross-scale importance of biotic and
abiotic “key structuring variables”:
• Essential analytical concept in ecological modeling
– e.g., state/transition models;
• Core principle in science of ecological integrity,
resistance & resilience
– resistance and resilience as consequences of feedback
relationships among key structuring variables
• Core principle in development of ecosystem
management “score-cards” or “report cards
Theory (1):
“Acceptable range of variation”
• Natural variation in key attributes crucial...
– as driver of species adaptations
– as engine of biological evolution and ecosystem
transformation
– as engine of disturbances that maintain ecological
heterogeneity over time/space
• Concept of “ARV” places emphasis on limits of
range, not the details
– limits to both “normal” and extreme variation
– crossing these limits puts target persistence at risk
(population extinction, system transformation)
Theory (2):
“Acceptable range of variation”
Species
Community/
Ecological
System
Theory (3):
“Acceptable range of variation”
Foundation: cross-scale principles of population and
ecosystem variability & persistence
• Ecological systems exhibit variation in c/s/f within “domains
of stability/variability” (rather than equilibration)
– managing for persistence within limits of domain
as best management strategy
– catastrophic transformation as consequence of crossing limits
• Persistence of ecological systems involves …
– resistance to the potential of disturbances to push conditions
outside the limits of domain
– resilience - ability to recover - upon being pushed out
• Population “floor and ceiling” models as equivalents for
individual species
Conceptual challenges
• What is/are the appropriate time-scale(s) to consider, when
identifying key ecological attributes for a target?
• How can we be sure we have identified truly “key” ecological
attributes and “critical” thresholds to their ARV?
• How do we recognize and address possible differences between
degradation and restoration (or recovery) thresholds?
• How useful are data on the “historic range of variation” in
setting goals for an attribute?
• How do we select indicators that best best track each key
attribute?
• How do we accommodate the existence of multiple alternative
ecosystem states?
• Should we treat human activities and non-native species as
components of the target or as threats?
Challenges (1):
Appropriate
time-scales
“Mesoscale
“50-100 years”?
Challenges (2): What is “key” or
“critical”?
• “Key” attributes are not simply any variables, but
pivotal ones, that…
– highly constrain many others
– dominate dynamics of target
– establish thresholds for entire domains of stability
• Therefore assumes a hierarchy of variables
– modeling task is to identify this hierarchy
– and this has implications for time/space scale of model
• “Critical” thresholds (limits to ARV) therefore
assumed to be limits to dominant variables
degradation
Key Attribute Y
(e.g., an attribute of a composition)
Challenges (3): Degradation vs.
recovery thresholds
restoration
Key Attribute X
(e.g., an attribute of a fire regime)
Challenges (4): “Natural” versus
acceptable range of variation
• Historical record of “natural” variation has limited
usefulness, even when available...
– limited in time depth/scale
– limited in comparability to current (often novel) systems
• Historical record best viewed as a source for
developing hypotheses, alongside others:
–
–
–
–
experts
reference occurrences
analogs (with varying human impacts)
models
Conclusions
• Strong basic scientific foundation for new “viability”
framework - but in an evolving science
• As this foundation evolves, so should framework
• Even with its strong foundation, framework entails
several assumptions and areas of uncertainty
• Implementation of framework therefore offers
opportunity to improve basic conservation science,
through an institution-wide experiment
Further information
Parrish JD, Braun DP, Unnasch RS. 2003. “Are We Conserving
What We Say We Are? Measuring Ecological Integrity
Within Protected Areas”. BioScience, in press.